8346836: C2: Introduce a way to verify the correctness of ConstraintCastNodes at runtime

src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -837,6 +837,42 @@ void C2_MacroAssembler::fast_unlock_lightweight(Register obj, Register reg_rax,
   // C2 uses the value of ZF to determine the continuation.
 }
 
+#ifdef ASSERT
+void C2_MacroAssembler::checked_cast_int(const TypeInt* type, Register dst) {
+  Label fail;
+  Label succeed;
+  cmpl(dst, type->_lo);
+  jccb(Assembler::less, fail);
+  cmpl(dst, type->_hi);
+  jccb(Assembler::lessEqual, succeed);
+  bind(fail);
+  stop("Invalid CastII");
+  bind(succeed);
+}
+
+void C2_MacroAssembler::checked_cast_long(const TypeLong* type, Register dst, Register tmp) {
+  Label fail;
+  Label succeed;
+  if (is_simm32(type->_lo)) {
+    cmpq(dst, checked_cast<int>(type->_lo));
+  } else {
+    mov64(tmp, type->_lo);
+    cmpq(dst, tmp);
+  }
+  jccb(Assembler::less, fail);
+  if (is_simm32(type->_hi)) {
+    cmpq(dst, checked_cast<int>(type->_hi));
+  } else {
+    mov64(tmp, type->_hi);
+    cmpq(dst, tmp);
+  }
+  jccb(Assembler::lessEqual, succeed);
+  bind(fail);
+  stop("Invalid CastLL");
+  bind(succeed);
+}
+#endif // ASSERT
+
 //-------------------------------------------------------------------------------------------
 // Generic instructions support for use in .ad files C2 code generation
 

src/hotspot/cpu/x86/c2_MacroAssembler_x86.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -44,6 +44,11 @@
                              Register t, Register thread);
   void fast_unlock_lightweight(Register obj, Register reg_rax, Register t, Register thread);
 
+#ifdef ASSERT
+  void checked_cast_int(const TypeInt* type, Register dst);
+  void checked_cast_long(const TypeLong* type, Register dst, Register tmp);
+#endif
+
   // Generic instructions support for use in .ad files C2 code generation
   void vabsnegd(int opcode, XMMRegister dst, XMMRegister src);
   void vabsnegd(int opcode, XMMRegister dst, XMMRegister src, int vector_len);

src/hotspot/cpu/x86/x86_64.ad

@@ -1,5 +1,5 @@
 //
-// Copyright (c) 2003, 2024, Oracle and/or its affiliates. All rights reserved.
+// Copyright (c) 2003, 2025, Oracle and/or its affiliates. All rights reserved.
 // DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 //
 // This code is free software; you can redistribute it and/or modify it
@@ -6991,6 +6991,7 @@ instruct castPP(rRegP dst)
 
 instruct castII(rRegI dst)
 %{
+  predicate(!VerifyConstraintCasts);
   match(Set dst (CastII dst));
 
   size(0);
@@ -7000,8 +7001,22 @@ instruct castII(rRegI dst)
   ins_pipe(empty);
 %}
 
+instruct castII_checked(rRegI dst, rFlagsReg cr)
+%{
+  predicate(VerifyConstraintCasts);
+  match(Set dst (CastII dst));
+
+  effect(KILL cr);
+  format %{ "# checked_cast_II $dst" %}
+  ins_encode %{
+    DEBUG_ONLY(__ checked_cast_int(bottom_type()->is_int(), $dst$$Register));
+  %}
+  ins_pipe(pipe_slow);
+%}
+
 instruct castLL(rRegL dst)
 %{
+  predicate(!VerifyConstraintCasts);
   match(Set dst (CastLL dst));
 
   size(0);
@@ -7011,6 +7026,19 @@ instruct castLL(rRegL dst)
   ins_pipe(empty);
 %}
 
+instruct castLL_checked(rRegL dst, rRegL tmp, rFlagsReg cr)
+%{
+  predicate(VerifyConstraintCasts);
+  match(Set dst (CastLL dst));
+
+  effect(KILL cr, TEMP tmp);
+  format %{ "# checked_cast_LL $dst" %}
+  ins_encode %{
+    DEBUG_ONLY(__ checked_cast_long(bottom_type()->is_long(), $dst$$Register, $tmp$$Register));
+  %}
+  ins_pipe(pipe_slow);
+%}
+
 instruct castFF(regF dst)
 %{
   match(Set dst (CastFF dst));

src/hotspot/share/opto/c2_MacroAssembler.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2022, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -31,6 +31,8 @@
 #include "utilities/macros.hpp"
 
 class C2EntryBarrierStub;
+class TypeInt;
+class TypeLong;
 
 class C2_MacroAssembler: public MacroAssembler {
  public:

src/hotspot/share/opto/c2_globals.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2000, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2000, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -660,6 +660,10 @@
   develop(bool, VerifyAliases, false,                                       \
           "perform extra checks on the results of alias analysis")          \
                                                                             \
+  develop(bool, VerifyConstraintCasts, false,                               \
+          "perform runtime check to verify the value of a "                 \
+          "ConstraintCast lies inside its type")                            \
+                                                                            \
   product(intx, MaxInlineLevel, 15,                                         \
           "maximum number of nested calls that are inlined by high tier "   \
           "compiler")                                                       \

src/hotspot/share/opto/castnode.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2014, 2024, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2014, 2025, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -506,6 +506,12 @@ const Type* ConstraintCastNode::widen_type(const PhaseGVN* phase, const Type* re
   if (!phase->C->post_loop_opts_phase()) {
     return res;
   }
+
+  // Keep these casts for verification
+  if (VerifyConstraintCasts) {
+    return res;
+  }
+
   const TypeInteger* this_type = res->is_integer(bt);
   const TypeInteger* in_type = phase->type(in(1))->isa_integer(bt);
   if (in_type != nullptr &&